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Cardiovascular Block: Week 7 > The Common Trisomies (Chromosome Disorders 1) > Flashcards

The Common Trisomies (Chromosome Disorders 1) Flashcards

1
Q

What proportion of spontaneous miscarriages are due to chromosome abnormalities?

A

~50%

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2
Q

What proportion of stillbirths are due to chromosome abnormalities?

A

5%

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3
Q

What proportion of mental retardation is due to chromosome abnormalities?

A

10%

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4
Q

What proportion of live births are found to have significant chromosome abnormalities?

A

0.5-1%

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5
Q

Chromosome abnormalities may be divided into what two categories?

A
  1. Numerical

2. Structural

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6
Q

What types of structural chromosome disorders are there?

A
  • Translocations
  • Deletions
  • Duplications
  • Insertions
  • Inversions
  • Ring Chromosomes
  • Isochromosomes
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7
Q

What are the three types of translocations?

A
  1. Balanced
  2. Unbalanced
  3. Robertsonian
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8
Q

What does a deletion result in?

A

Creates a partial monosomy (when pieces of chromosomes are missing)

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9
Q

What does duplication result in?

A

Creates partial trisomy (when pieces of chromosomes are added)

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10
Q

What is a reciprocal translocation?

A

Balanced translocation,

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11
Q

What is the result of a balanced translocation in an individual?

A

For the carrier, there is no loss or addition of genetic material.
- Phenotypically expected to be normal

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12
Q

What may occur in the offspring of an individual with a balanced translocation?

A

Offspring may be at risk to inherit an unbalanced chromosome complement
- expected to exhibit an abnormal phenotype

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13
Q

What are the consequences of a duplication / deletion?

A

The consequences of a duplication or deletion are determined by the size of the involved segment, the number and type of genes involved and on occasion by the breakpoint.
- Not all deletions / duplications are “pathogenic” some are thought to be benign variants and are not thought to have significant phenotypic consequences.

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14
Q

What are the two types of numerical chromosomal abnormalities?

A
  1. Polyploidy

2. Aneuploidy

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15
Q

What are the two types of aneuploidy?

A
  1. Trisomy

2. Monosomy

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16
Q

What is trisomy?

A

“Too many” chromosomes - 47 chromosomes

e.g. Trisomy 13, 18, 21

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17
Q

What is monosomy?

A

“Too few” chromosomes - 45 chromosomes

e.g. Turner syndrome

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18
Q

What is polyploidy?

A

An “extra set” of chromosomes - 69 chromosomes

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19
Q

What are the majority of chromosome abnormalities due to?

A

Non-disjunction

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20
Q

What proportion of Trisomy 13 pregnancies result in spontaneous abortion?

A

95%

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21
Q

What proportion of Trisomy 18 pregnancies result in spontaneous abortion?

A

95%

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22
Q

What proportion of Trisomy 21 pregnancies result in spontaneous abortion?

A

80%

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23
Q

What proportion of Monosomy X pregnancies result in spontaneous abortion?

A

98%

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24
Q

What is the most common genetic cause of intellectual disability worldwide?

A

Down Syndrome (Trisomy 21)

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25
Q

What causes an increased risk of Down Syndrome?

A

Increase risk with increased maternal age:

  • Age 25 = 1/1350
  • Age 40 = 1/100
  • Age 45 = 1/30
26
Q

Which ethnic group is at greatest risk for Down Syndrome?

A

All ethnic groups are equally affected

27
Q

What are the three mechanisms by which Down Syndrome may be caused?

A
  1. Non-dysjunction (95%)
  2. Translocation (4%)
  3. Mosaicism (1%)
28
Q

What craniofacial abnormalities are seen in Down Syndrome?

A
  • flat facial profile and nasal bridge
  • bradycephaly
  • epicanthic folds
  • upslanted eyes
  • protruding tongue (less frequent in African patients)
  • small, low set ears
29
Q

What CNS abnormalities are seen in Down Syndrome?

A
  • hypotonia

- global developmental delay / intellectual disability (Ave IQ 45-48)

30
Q

What limb abnormalities are seen in Down Syndrome?

A
  • single palmar crease
  • clinodactyly
  • sandle-gap
  • bradydactyly
31
Q

What proportion of Down Syndrome patient’s have cardiac abnormalities?

A

40-50%

32
Q

What cardiac abnormalities are seen in Down Syndrome?

A
  • AVSD (40% - one of the commonest)
  • VSD
  • ASD
  • PDA
  • Tetralogy of Fallot
33
Q

What other abnormalities are seen in Down Syndrome?

A
  1. GIT (duodenal atresia, Hirschprungs disease)
  2. Visual problems
  3. Short stature
  4. Undescended testes, small penis
34
Q

What are some of the complications of Down Syndrome?

A
  • Atlanto-axial instability
  • Recurrent infections = conductive hearing loss
  • Cataracts
  • Transient neonatal ‘leukemia’
  • ALL (20x greater risk)
  • Hypothyroidism (20-40%) due to antibodies
  • Alzheimer Disease (8% by 49 years; 75% by 60 years)
35
Q

What is the life expectancy of Down Syndrome patients?

A

Depends on where you live, first world kids live a lot longer.

36
Q

What can be used to diagnose Down Syndrome?

A
  1. Chromosome analysis

2. PCR Aneuploidy Screen (QF-PCR)

37
Q

What are the recurrence risks for Down Syndrome in Non-dysjunction (<35 years)?

A

1%

38
Q

What are the recurrence risks for Down Syndrome in Non-dysjunction (>35 years)?

A

Age related risk

39
Q

What are the recurrence risks for Down Syndrome with a maternal translocation carrier?

A

10-15%

40
Q

What are the recurrence risks for Down Syndrome with a paternal translocation carrier?

A

1-3%

41
Q

What are the recurrence risks for Down Syndrome with a maternal translocation carrier, if the father is a 21q21q carrier?

A

100%

42
Q

What should be done medically to treat Down Syndrome?

A
  1. Annual thyroid function tests
  2. Growth monitoring
  3. Treat infections / other complications
  4. Surgery may be necessary: cardiac, GIT
  5. Neurodevelopmental interventions
  6. Psychosocial support and genetic counseling
43
Q

What growth charts should be used for Down Syndrome patients?

A

Normal growth charts (no longer use Down’s charts)

44
Q

What should be done for the neurodevelopmental management of Down Syndrome patients?

A
  1. Annual hearing / vision assessments
  2. Physio / OT / speech therapy
  3. Remedial schooling
45
Q

What is Patau Syndrome?

A

Trisomy 13

46
Q

What is the prevalence of Patau syndrome?

A

1/5000 live births, 2% of miscarriages

47
Q

What are the three genetic causes of Patau syndrome?

A
  1. Non-dysjunction (75%)
  2. Robertsonian translocation (20%)
  3. Mosaicism (5%)
48
Q

What increases the risk of Patau syndrome?

A

Maternal age related risks

49
Q

What can be seen in a fetus with Patau syndrome?

A

Antenatal abnormalities - 90% should be detected on ultrasound evaluation

50
Q

What are the features of Patau syndrome at birth?

A
  • scalp defects (50%)
  • central cleft lip, cleft palate
  • bulbous nose, post-axial polydactyly
  • polycystic kidneys
51
Q

What is the life expectancy of an infant with Patau syndrome?

A
  • 85% die in the 1st year

- rarely survive >3 years

52
Q

What is Trisomy 18?

A

Edwards Syndrome

53
Q

What is the prevalence of Edward’s Syndrome?

A

1/5000 live births, 3% of miscarriages

54
Q

What are the three causes of Edward’s Syndrome?

A
  1. Non-dysjunction trisomy (85%)
  2. Translocation (5%)
  3. Mosaicism (10%)
55
Q

What increases the risk of Edward’s Syndrome?

A

Maternal age related risks

56
Q

What are some of the features of Trisomy 18?

A
  • Often significant IUGR
  • Increased incidence of congenital anomalies: cardiac, renal, CNS
  • Microcephaly, micrognathia
  • Overlapping fingers
  • Limb abnormalities
  • Rocker bottom feet
57
Q

What can be done to prevent aneuploidy at a primary prevention level?

A

Antenatal care, family planning, AMA counseling

58
Q

What can be done to prevent aneuploidy at a secondary prevention level?

A

Screening for aneuploidy, fetal ultrasound assessments, invasive prenatal testing, TOP

59
Q

What can be done to prevent aneuploidy at a tertiary prevention level?

A

Reducing complications; surgical intervention, remedial intervention

60
Q

What is the difference in tone abnormalities between Trisomy 21 and Trisomy 18?

A

Trisomy 21 = hypotonic

Trisomy 18 = hypertonic

Cardiovascular Block: Week 7 (5 decks)

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